Lubricity additives for fuel oil compositions

ABSTRACT

Specific substituted aromatic amine salt compounds are useful as lubricity additives for middle distillate fuel oils.

This invention relates to additives for improving the lubricity of fueloils such as diesel fuel oil. Diesel fuel oil compositions including theadditives of this invention exhibit improved lubricity and reducedengine wear.

Concern for the environment has resulted in moves to significantlyreduce the noxious components in emissions when fuel oils are burnt,particularly in engines such as diesel engines. Attempts are being made,for example, to minimise sulphur dioxide emissions. As a consequenceattempts are being made to minimise the sulphur content of fuel oils.For example, although typical diesel fuel oils have in the pastcontained 1% by weight or more of sulphur (expressed as elementalsulphur) it is now considered desirable to reduce the level to 0.2% byweight, preferably to 0.05% by weight and, advantageously, to less than0.01% by weight, particularly less than 0.001% by weight.

Additional refining of fuel oils, necessary to achieve these low sulphurlevels, often results in reductions in the level of polar components. Inaddition, refinery processes can reduce the level of polynucleararomatic compounds present in such fuel oils.

Reducing the level of one or more of the sulphur, polynuclear aromaticor polar components of diesel fuel oil can reduce the ability of the oilto lubricate the injection system of the engine so that, for example,the fuel injection pump of the engine fails relatively early in the lifeof an engine. Failure may occur in fuel injection systems such as highpressure rotary distributors, in-line pumps and injectors. The problemof poor lubricity in diesel fuel oils is likely to be exacerbated by thefuture engine developments aimed at further reducing emissions, whichwill have more exacting lubricity requirements than present engines, Forexample, the advent of high pressure unit injectors is anticipated toincrease the fuel oil lubricity requirement.

Similarly, poor lubricity can lead to wear problems in other mechanicaldevices dependent for lubrication on the natural lubricity of fuel oil.

Lubricity additives for fuel oils have been described in the art. WO94/17160 describes an additive which comprises an ester of a carboxylicacid and an alcohol wherein the acid has from 2 to 50 carbon atoms andthe alcohol has one or more carbon atoms. Glycerol monooleate isspecifically disclosed as example. Acids of the formula “R¹ (COOH)”,wherein R¹ is an aromatic hydrocarbyl group are generically disclosedbut not exemplified.

U.S. Pat. No. 3,273,981 discloses a lubricity additive being a mixtureof A+B wherein A is a polybasic acid, or a polybasic acid ester made byreacting the acid with C1-C5 monohydric alcohols; while B is a partialester of a polyhydric alcohol and a fatty add, for example glycerolmonooleate, sorbitan monooleate or pentaerythritol monooleate. Themixture finds application in jet fuels.

GB-A-1,505,302 describes ester combinations including, for example,glycerol monoesters and glycerol diesters as diesel fuel additives, thecombinations being described as leading to advantages including lesswear of the fuel-injection equipment, piston rings and cylinder liners.GB-A-1,505,302 is, however, concerned with overcoming the operationaldisadvantages of corrosion and wear by acidic combustion products,residues in the combustion chamber and in the exhaust system. Thedocument states that these disadvantages are due to incompletecombustion under certain operating conditions. Typical diesel fuelsavailable at the date of the document contained, for example, from 0.5to 1% by weight of sulphur, as elemental sulphur, based on the weight ofthe fuel.

U.S. Pat. No. 3,287,273 describes lubricity additives which are reactionproducts of a dicarboxylic acid and an oil-insoluble glycol. The acid istypically predominantly a dimer of unsaturated fatty acids such aslinoleic or oleic acid, although minor proportions of the monomer acidmay also be present. Only alkane diols or oxa-alkane diols arespecifically suggested as the glycol reactant.

U.S. Pat. No. 4,090,971 and EP-A0 719 761 describe certain amides ofsubstituted hydoxyaromatic carboxylic acids, these materials beingdescribed as useful as dispersant additives for lubricants and fuels,respectively. No mention is made of low sulphur middle distillate fuelsor how to solve their corresponding problem of poor lubricity.

U.S. Pat. No. 5,089,158 describes derivatives of amides of an aromaticcarboxylic acid having an ortho-hydroxy group in the form of a salt witha multivalent metal ion, formed from amide precursors via an esterintermediate. The salts so formed are preferably overbased.

EP-A-0 663 898 describes certain compounds having the formula;

wherein B represents an aromatic system, A represents a hydrocarbylgroup, R¹ and R² are the same or are different and each independently isan aliphatic hydrocarbyl group containing 10 to 40 carbon atoms, z is atleast 1 and wherein the aromatic system carries at least one activatinggroup which may be a hydroxyl group. The aromatic system may also carrya substituent of general formula:

wherein w=0 or 1 and Q represents A, Such materials are described ascold flow-improving additives for middle distillate fuels.

There exists in the art a continual need for lubricity additives showingenhanced performance, due not only to the development of engines withmore exacting requirements, but also to the general demand fromconsumers and fuel producers for higher quality fuels.

Furthernore, there is an increasing need in the art for‘multifunctional’ additive compositions. Such compositions provide arange of performance—enhancing functions, typically through theincorporation therein of a number of individual additives each havingits own function. The resulting complex mixtures often require additionto the fuel in relatively large amounts, and may also suffer fromproblems of physical and chemical interaction between individualadditives which can impair their subsequent performance in the fuel. Theprovision of an individual additive with multiple performance enhancingeffects can reduce or avoid the need for such complex compositions andtheir associated problems.

It has now been found that certain amine salts of specific substitutedaromatic carboxylic acids show lubricity performance. Some of theseamine salts may also impart other performance enhancing effects tolow-sulphur fuel oils.

In a first aspect, this invention provides a fuel oil compositionobtainable by the addition of a minor proportion of a compoundcomprising one or more aromatic ring systems wherein at least one of thering systems bears, as substituents;

(i) one or more hydrocarbon groups imparting oil solubility to thecompound, and

(ii) one or more hydroxyl groups or derivatives thereof or both, and

(iii) one or more amine salt groups to a major proportion of a liquidhydrocarbon middle distillate fuel oil having a sulphur concentration of0.2% by weight or less, based on the weight of fuel.

In a second aspect, this invention provides a fuel oil compositionobtainable by the addition, to the fuel oil defined under the firstaspect, of an additive composition or concentrate into which has beenincorporated the compound defined under the first aspect.

In a third aspect, this invention provides a compound comprising one ormore aromatic ring systems, wherein at least one of the ring systemsbears, as substituents;

(i) one or more hydrocarbon groups imparting oil solubility to thecompound, and

(ii) one or more hydroxyl derivatives of the formula —OR′ wherein R′ ishydrocarbyl or a group of the formula

wherein M represents an oxygen atom or an NH group and n represents anumber from 1 to 50, and

(iii) one or more amine salt groups.

Further aspects of this invention include an additive composition intowhich has been incorporated the compound of the third aspect, and anadditive concentrate obtainable by incorporating the compound oradditive composition and optionally one or more additional additives,into a mutually-compatible solvent therefore.

The compounds defined under the first aspect of the invention provide,upon addition to low sulphur middle distillate fuel oil, an improvementin fuel oil lubricity.

In particular, the specific compounds defined under the first aspect,including those compounds claimed under the third aspect, give higherlubricity performance even at treat rates as low as 15 to 50 parts permillion by weight, per weight of fuel oil. Furthermore, some of thesecompounds may impart other performance—enhancing features to fuel oils,particularly detergency of engine fuel inlet systems and especially fuelinjectors, reduced oxidation tendency especially during storage, and theability to disperse insolubles which might otherwise give rise toharmful deposits and/or fuel line blockages. The detergency anddispersancy advantages may be apparent for those components wherein oneor more of the substituents (ii) is a derivative of a hydroxyl group ofthe formula OR′ as hereinafter described.

THE FUEL OIL COMPOSITION OF THE FIRST ASPECT OF THE INVENTION A. TheCompound

The compound may comprise one or more aromatic ring systems. By‘aromatic ring system’ in this specification is mean a planar cyclicmoiety which may be an aromatic homocyclic, heterocyclic or fusedpolycyclic assembly or a system where two or more such cyclic assembliesare joined to one another and in which the cyclic assemblies may be thesame or different. It is preferred that the or each aromatic ring systemis system based on heterocyclic or homocyclic 5- or 6-membered rings,more preferably 6-membered rings and most preferably benzene rings.

The ring atoms in the aromatic system are preferably carbon atoms butmay for example include one or more heteroatoms such as N, S, or O inthe system in which case the compound is a heterocyclic compound.

Examples of suitable polycyclic assemblies include

(a) condensed benzene structures such as naphthalene, anthracene,phenanthrene, and pyrene;

(b) condensed ring structures where none of or not all of the rings arebenzene such as azulene, indene, hydroindene, fluorene, and diphenylene;

(c) rings joined “end-on” such as biphenyl; and

(d) heterocyclic compounds such as quinoline, indole, 2:3dihydroxyindole, benzofuran, benzothiophen, carbazole andthiodiphenylamine.

Where the compound comprises only one aromatic ring system, this systemnecessarily bears all three types of substituent (i), (ii) and (iii). Itis preferred that one of each of the substituents (ii) and (iii) ispresent in such a compound. It is also preferred that one, two or threesubstituents (i) are present, at least one of which is capable ofimparting oil solubility to the compound.

Where the compound comprises two or more aromatic ring systems, it ispreferred that at least two, and preferably each, of the systems bearsall three types of substituent (i), (ii) and (iii). It is preferred thateach system bearing these three types of substituents bears one of eachof substituent (ii) and (iii), and preferably one, two or threesubstituents (i), subject to the requirement that at least one of thesubstituents (i) provides oil solubility to the compound.

Particularly preferred are compounds wherein the or each aromatic ringsystem is a single, 6-membered ring, especially a benzene structure.Most preferably, tho compound comprises a single benzene ring and one,two or three (preferably one or two) of the substituents (i) and havingone of each of the (ii) and (iii) subsituents, wherein substituent (ii)is a hydroxyl group.

Substituent (i) is a hydrocarbon group. By the term hydrocarbon as usedin this specification in relation to substituent (i) is meant an organicmoiety which is composed of hydrogen and carbon only, which is bonded tothe rest of the molecule by a carbon atom or atoms and which unless thecontext states otherwise, may be aliphatic, including alicyclic,aromatic or a combination thereof. It may be substituted orunsubstituted alkyl, aryl or alkaryl optionally contain unsaturation.

It is preferred that substituent (i) is aliphatic, for example alkyl oralkenyl, which may be branched or preferably straight-chain.Straight-chain alkyl is preferred.

It is essential for the good performance of the compound that at leastone substituent of the formula (i) be a hydrocarbon group of sufficientoleophilic character to impart oil solubility to the compound. In thisrespect, it is preferred that at least one substituent (i) contains atleast 8 carbon atoms, and preferably 10 to 200 carbon atoms. Asubstituent having 12 to 54, for example 14 to 36 carbon atoms isparticularly preferred. Most preferred are alkyl or alkenyl groupscontaining 12 to 54 carbon atoms, especially straight chain alkylgroups. The groups having 14 to 20 carbon atoms are most advantageous.

Provided that the compound possesses at least one hydrocarbonsubstituent (i) imparting the requisite oil solubility, any additionalsubstituents (i) may be of any character provided that they do notadversely interfere with the oil solubility of the compound.

Substituent (ii) is a hydroxyl group or derivative thereof, and can berepresented by the formula —OR′. When a hydroxyl group, the compound mayshow particularly good performance as an oxidation inhibitor

The hydroxyl group may be derivatised into a substituent capable ofimparting other multifuctional character, for example a group of theform —OR′ wherein R′ is hydrocarbyl, or a linear or branched chainalkyleneoxyhydrocarbyl or poly(alkyleneoxy)hydrocarbyl group and/or alinear or branched chain alkyleneaminohydrocarbyl orpoly(alkyleneamino)hydrocarbyl group having the formula:

wherein M represents a oxygen atom or an NH group and n represents anumber from 1 to 50, preferably 2 to 20, more preferably 2 to 10, forexample 3 to 5.

By the term hydrocarbyl in this specification is meant an organic moietywhich is composed of hydrogen and carbon and which is bonded to the restof the molecule by a carbon atom or atoms and which includes hydrocarbongroups as hereinbefore defined in relation to substituent (i), as wellas predominantly hydrocarbon groups also containing heteroatoms such asO, N or S provided that such heteroatoms are insufficient to alter theessentially hydrocarbon nature of the group. The hydrocarbyl group insubstituent (ii) may especially be substituted, preferably terminallysubstituted, by a heteroatom-containing group, for example it a hydroxylor amino group. Small hydrocarbyl groups, such as those containing 1 to24, preferably 1 to 18, for example 2 to 12 carbon atoms areparticularly advantageous. The alkylene group may contain 1 to 6, forexample 2 to 4 methylene units and may also optionally be substituted bysuch a heteroatom containing group or groups. R′ may be bonded directlyto the oxygen depending from the ring system or indirectly via a linkinggroup, such as a carbonyl group. The heteroatom-containing derivativesof the hydroxyl group, useful as substituent (ii), may proveparticularly beneficial in providing dispersant and/or detergentproperties when used in fuel oils. Preferred in this respect arederivatives of the formula

wherein n′ represents a number from 1 to 24, preferably 1 to 18, morepreferably 1 to 6, preferably 3.

Substituent (iii) is an amine salt group, wherein the carbonyl carbon ofthe amide is preferably bonded directly to a ring atom of the aromaticring system and more preferably to a ring carbon. The amine salt groupis preferably of the formula:

wherein the cation ^(⊕)NR^(2′)R^(3′)R^(4′)R^(5′)is derivable from thecorresponding amine NR^(2′)R^(3′)R^(4′), wherein R^(2′), R^(3′) and R⁴′each independently represent a hydrogen or hydrocarbyl group aspreviously defined, and especially one having 1 to 30, for example 1 to22, carbon atoms and optionally substituted by heteroatoms orheteroatom—containing groups, or R^(2′), R^(3′) and R^(4′) eachindependently represent a poly(alkyleneoxy)alkyl orpoly(alkyleneamino)alkyl group, also optionally so substituted. R^(5′)may represent hydrogen or a group as hereinbefore defined in relation toR^(2′), R^(3′) or R^(4′).

Preferably at least one, and more preferably the or each substituent(iii), is derivable from a primary or secondary amine or compoundcontaining at least one primary or secondary amine group Thus, forexample, where the substituent (iii) is of the formula

two or three of the R^(2′), R^(3′), R^(4′) and R^(5′) substituents inthe amine salt group are hydrogen. The or each remaining substituent ispreferably a hydrocarbyl group, or an amino-interrupted and/oramino-substituted hydrocarbyl group, wherein the hydrocarbyl group ispreferably alkyl, more preferably n-alkyl. Such amine salts arederivable for example from amines such as mono- and di-hydrocarbylamines, hydrocarbylene diamines and polyhydrocarbylene polyamines havingat least one primary amine group. Examples include mono- and dialkylamines, in which each alkyl group has from 8 to 40 carbon atoms.Dihydrogenated tallow-amine is one example. Other amino groups, wherepresent, may be primary, secondary or tertiary amino groups. Such aminesmay suitably also be substituted by other heteroatom-containing groups,such as hydroxy-groups or derivatives thereof.

A tertiary amine, for example trimethylamine, may also be used,

For example, the amine from which the amine salt group is derivable maybe an alkylene diamine. Such diamines may contain one or two preferablyprimary amino groups and between 1 and 50, for example 2 to 10,preferably 2 to 6 carbon atoms preferably in a straight alkylene chain.Where the diamine contains one primary amino group, the other group maybe a secondary or tertiary amino group. Examples includeN,N-dimethyl-1,3-propanediamine; N,N-dimethyl-1,2-propanediamine:N,N-dimethyl-1,2-ethanediamine; and their N,N-diethyl and N,N-dipropylsubstituted homologues. N,N-dimethyl-1,3-propanediamine is preferred.

Where the diamine contains two primary groups, examples include1,2-ethanediamine; 1,2- and 1,3-propanediamines; and 1,2-, 1,3- and1,4-butanediamines. 1,2-ethanediamine is most preferred.

The amine from which the amine salt group is derivable may be apolyalkylene polyamine. Suitable amines include those containing one ortwo amino groups and between 2 and 50, for example 4 and 20 carbonatoms, and preferably between 6 and 12 carbon atoms, preferably in aseries of straight alkylene segments. Such amines include those of thegeneral formula

wherein alkylene represents a straight chain alkylene segment containingpreferably 2 to 4 carbon atoms, and x represents a number from 2 to 10,preferably 3 to 6. Mixtures of such polyalkylene polyamines, as aretypically produced commercially, may be used. Such mixtures may alsoadditionally contain polyamines in which ‘alkylene’ may representbranched chain or cyclic units.

Suitable polyalkylene polyamines are polyethylene polyamines such asdiethylene triamine, triethylene tetramine; tetraethylene pentamine andpentaethylene hexamine, and mixtures thereof. Mixtures are typicallydescribed by reference to the polyamine to which their averagecomposition approximates; thus, ‘a mixture approximating totetraethylene pentamine’ is one in which the average number of nitrogensper molecule of polyamine approximates to 5. Triethylene tetramine,tetraethylene pentamine and pentaethylene hexamine are preferred asamine materials useful for forming the amine salts of this invention,with pentamine mixtures being most preferred.

Polypropylene and polybutylene polyamine analogues, and mixturesthereof, are also suitable amines for forming the amine salts used inthis invention.

Other useful amines are polyhydroxyamines giving rise in the compound toamine salt groups comprising hydroxy—substituted alkyl substituents.Suitable polyhydroxy amines are aliphatic, saturated or unsaturated,straight chain or branched hydroxy amines having 2 to 10. Preferably 2to 6, more preferably 2 to 4, hydroxyl groups, and having 2 to 90,preferably 2 to 30, more preferably 2 to 12, most preferably 2 to 5,carbon atoms in the molecule,

In the compound, the substituents (ii) and (iii) are preferablypositioned vicinally on the aromatic ring system from which they depend.Where the system is polycyclic they are preferably positioned vicinallyon the same ring of the polyclinic system, for example in an orthoposition to each other, although they may be positioned on differentrings. The or each substituent (i) may be positioned vicinally to any ofthe subsituents (ii) or (iii), or in a position further removed in thering system.

The compound may also be of oligomeric structure, for example a seriesof aromatic ring systems connected via alkylene bridges produced, forexample, by the phenol-formaldehyde type condensation reaction ofseveral aromatic ring systems with aldehyde; or an oligomer containingtwo or more aromatic ring systems in which each ring is linked to adifferent nitrogen of the same di- or polyamine. Particularly useful aremethylene—bridged compounds wherein each aromatic ring system ispreferably a homocyclic, six-membered ring and wherein, more preferably,each ring carries at least one of each of the substituents (i), (ii) and(iii).

A preferred form of the compound can be represented by the followinggeneral formula (1):

wherein Ar represents an aromatic ring system, —B, —OR′ and—COO^(⊖⊕)NR^(2′)R^(3′)R^(4′)R^(5′) represent substituents (i), (ii) and(iii) respectively as hereinbefore defined, and A represents a group ofthe formula (II):

wherein Ar, B, R′, R^(2′), R^(3′), R^(4′) and R^(5′) are as hereinbeforedefined in formula (I) and A′ and A″ each independently representhydrocarbylene groups, and herein:

v represents an integer in the range of from 0 to 10;

w represents an integer in the range of from 0 to 3;

and x, y and z each independently represent an integer in the range offrom 1 to 3.

Preferably, R′ represents hydrogen, or a hydrocarbyl group, or apoly(alkyleneoxy)alkyl or poly(alkyleneamino)alkyl group optionallysubstituted by one or more heteroatom—containing groups, and wherein R′may be bonded either directly to the oxygen depending from the ringsystem, or indirectly via a linking group, R^(2′), R^(3′), R^(4′) andR^(5′) preferably independently represent hydrogen or a hydrocarbylgroup optionally substituted by one or more heteroatom—containinggroups, or a poly(alkyleneoxy) alkyl or poly(alkyleneamino)alkyl group,also optionally so substituted, or other preferments of R^(2′), R^(3′),R^(4′) and R^(5′) described hereinbefore.

Preferably, x represents 1 or 2, especially when y and z eachrepresent 1. When w is 1 to 3, v is preferably 1 to 9, for example 2 to5, such as 3. Alternatively, v maybe 0 (zero) A′ and A″ are preferablymethylene or substituted methylene groups.

When w=o, the compound comprises a single aromatic ring system havingsubstituents (i), (ii) and (iii). It is preferred that when w=o, y and zeach=1 and x=1 or 2; more preferably, R^(2′) represents an alkyl,alkylene amino or polyalkylenepolyamino group, R^(3′) represents R″ orhydrogen, R′, R^(4′) and R^(5′) represent hydrogen. Most preferably, Arrepresents a benzene ring; w=0; x=1 or 2; y and z each=1; R^(2′) andR^(3′) each represent a alkyl group and R′, R^(3′) and R^(5′) eachrepresent hydrogen.

Most preferably, the compound is an amine salt of alkyl-substitutedsalicylic acid, the alkyl substituent or substituents of the acidcontaining between 14 and 18 carbon atoms.

The mechanism of action of the compound is not clearly understood.However, it is postulated that the specific substituted aromatic ringsystem or systems form a flat region within the molecule, the hydroxylor hydroxyl-derivatised group and the amine salt group and substituentsof said group contributing to an electronic and polar character acrossthis flat region which is surprisingly effective at surface adsorptionand improving the fuels' ability to lubricate critical metal surfaces inthe injection system, and particularly in the injection pump.

The compound may be prepared by conventional means. Thus, for example,the compound may be prepared by reaction of a precursor compound havingthe requisite aromatic ring system or systems bearing substituent(s)(i), substituent(s) (ii) and one or more carboxylic acid substituentscapable of forming a salt, with compounds having at least one aminogroup to form substituent (iii).

The precursor compound may itself be prepared by hydrocarbylation of asuitable hydroxyl—substituted aromatic ring system compound, for exampleby an electrophilic substitution reaction using a halide derivative ofthe desired hydrocarbyl substituent(s), for example via a Friedel-Craftstype reaction using iron (iii) chloride as catalyst Alternatively,hydrocarbylation can be achieved through reaction of the correspondingalkene using a hydrogen fluoride and boron trifluoride catalyst system,or hydrogen chloride and aluminum trichloride catalyst system. Theresulting hydrocarbyl—substituted, hydroxyl—substituted aromaticcompound may be carboxylated, for example via the ‘Kolbe-Schmitt’reaction comprising the reaction of a salt, preferably an alkali metalsalt, of the hydrocarbyl substituted, hydroxyl—substituted aromaticcompound with carbon dioxide and subsequently acidifying the salt thusobtained. Alternatively, a Friedel-Crafts acylation-type reactionproduct may be used to add the required carboxylic acid substituent(s).The above types of reaction are well-known in the chemical art.

The preferred precursor compounds are carboxylic acid derivatisedhydrocarbyl—substituted phenols and/or napthols, with phenols being themost preferred. Particularly preferred are the hydrocarbyl—substitutedsalicylic acids, which typically comprise a mixture of mono anddisubstituted acids. These materials are readily available in a formsuitable for the reaction with amines, without the need for furthermodification.

B. The Middle Distillate Fuel Oil

The fuel oil has a sulphur concentration of 0.2% by weight or less basedon the weight of the fuel, and preferably 0.05% or less, more preferably0.03% or less, such as 0.01% or less, most preferably 0,005% or less andespecially 0.001% or less. Such fuels may be made by means and methodsknown in the fuel-producing art, such as solvent extraction,hydrodesulphurisation and sulphuric acid treatment.

As used in this specification, the term “middle distillate fuel oil”includes a petroleum oil obtained in refining crude oil as the fractionbetween the lighter kerosene and jet fuels fraction and the heavier fueloil fraction. Such distillate fuel oils generally boil within the rangeof about 100° C., eg 150° to about 400° C. and include those having arelatively high 95% distillation point of above 360° C. (measured byASTM-D86). In addition, “city diesel” type fuels, having lower 95%distillation point of 260-330° C. and particularly also sulphur contentsof less than 200 ppm, preferably 50 ppm and particularly 10 ppm(weight/weight) are included within the term ‘middle distillate fueloil’.

Middle distillates contain a spread of hydrocarbons boiling over atemperature range, including n-alkanes which precipitate as wax as thefuel cools. They may be characterized by the temperatures at whichvarious %'s of fuel have vaporized (‘distillation point’), e.g. 50%,90%, 95%, being the interim temperatures at which a certain volume % ofinitial fuel has distilled. They are also characterized by pour, cloudand CFPP points, as well as their initial boiling point (IBP) and 95%distillation point or final boiling point (FBP). The fuel oil cancomprise atmospheric distillate or vacuum distillate, or cracked gas oilor a blend in any proportion of straight run and thermally and/orcatalytically cracked distillates. The most common middle distillatepetroleum fuel oils are diesel fuels and heating oils. The diesel fuelor heating oil may be a straight atmospheric distillate, or it maycontain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or crackedgas oils or of both.

Heating oils may be made of a blend of virgin distillate, eg gas oil,naphtha, etc and cracked distillates, eg catalytic cycle stock. Arepresentative specification for a diesel fuel includes a minimum flashpoint of 38° C. and a 90% distillation point between 282 and 380° C.(see ASTM Designations D-396 and D-975).

As used in this specification, the term ‘middle distillate fuel oil’also extends to biofuels, or mixtures of biofuels with middle distillatepetroleum fuel oils.

Biofuels, ie fuels from animal or vegetable sources are believed to beless damaging to the environment on combustion, and are obtained from arenewable source. Certain derivatives of vegetable oil, for examplerapeseed oil, eg those obtained by saponification and re-esterificationwith a monohydric alcohol, may be used as a substitute for diesel fuel.It has recently been reported that mixtures of biofuels, for example,between 5:95 and 10:90 by volume are likely to be commercially availablein the near future.

Thus, a biofuel is a vegetable or animal oil or both or a derivativethereof.

Vegetable oils are mainly trigylerides of monocarboxylic acids, eg acidscontaining 10-25 carbon atoms and of the following formula:

wherein R is an aliphatic radical of 10-25 carbon atoms which may besaturated or unsaturated.

Generally, such oils contain glycerides of a number of acids, the numberand kind varying with the source vegetable of the oil,

Examples of oils are rapeseed oil, coriander oil, soyabean oil,cottonseed oil, sunflower oil, castor oil, olive oil, peanut oil, maizeoil, almond oil, palm kernel oil, coconut oil, mustard seed oil, beeftallow and fish oils. Rapeseed oil, which is a mixture of fatty acidsparticularly esterified with glycerol, is preferred as it is availablein large quantities and can be obtained in a simple way by pressing fromrapeseed.

Examples of derivatives thereof are alkyl esters, such as methyl esters,of fatty acids of the vegetable or animal oils. Such esters can be madeby transesterification.

As lower alkyl esters of fatty acids, consideration may be given to thefollowing, for example as commercial mixtures: the ethyl, propyl, butyland especially methyl esters of fatty acids with 12 to 22 carbon atoms,for example of lauric acid, myristic acid, palmitic acid, palmitoleicacid, stearic acid, oleic acid, petroselic acid. ricinoleic acid,elaeostearic acid, linoleic acid, linolenic acid, elcosanoic acid,gadoleic acid, docosanoic acid or erucic acid, which have an iodinenumber from 50 to 150, especially 90 to 125. Mixtures with particularlyadvantageous properties are those which contain mainly, ie. to at least50 wt % methyl esters of fatty adds with 16 to 22 carbon atoms and 1, 2or 3 double bonds. The preferred lower alkyl esters of fatty acids arethe methyl esters of oleic acid, linoleic add, linolenic acid and erucicacid.

Commercial mixtures of the stated kind are obtained for example bycleavage and esterfication of natural fats and oils by theirtransesterification with lower aliphatic alcohols. For production oflower alkyl esters of fatty acids it is advantageous to start from fatsand oils with high iodine number, such as, for example, sunflower oil,rapeseed oil, coriander oil, castor oil, soyabean oil, cottonseed oil,peanut oil or beef tallow. Lower alkyl esters of fatty acids based on anew variety of rapeseed oil, the fatty acid component of which isderived to more that 80 wt % from unsaturated fatty acids with 18 carbonatoms, are preferred.

The above described biofuels may be used in blends with middledistillate petroleum fuel oils Such blends typically contain 0 to 10% byweight of the biofuel and 90 to 100% by weight of the petroleum fueloil, although other relative proportions may also be used toadvantageous effect. Particularly useful are blends of biofuels with‘city diesel’ type fuel oils which exhibit extremely low levels ofsulphur and are therefore particularly prone to lubricity problems.

In the fuel oil composition of the first aspect, the concentration ofthe compound incorporated into the oil may for example be in the rangeof 0.5 to 1,000 ppm of additive (active ingredient) by weight per weightof fuel, for example 1 to 500 ppm such as 10 to 200 ppm by weight perweight of fuel, preferably 20 to 200 ppm, more preferably 25 to 100 ppm.

In addition to middle distillate fuel oils, other fuels having a needfor increased lubricity, such as fuels (eg. future gasoline) intendedfor high pressure fuel injection equipment, may suitably be treated withthe additives of the invention.

THE FUEL OIL COMPOSITION OF THE SECOND ASPECT OF THE INVENTION C. TheAdditive Composition

The additive composition defined under the second aspect is prepared bythe incorporation of the compound as defined under the first aspect intoa composition itself comprising one or more additives for fuel oils.Such incorporation may be achieved by blending or mixing, either with anexisting composition or with the components thereof, to produce theadditive, However, the term ‘Incorporation’ within the meaning of thisspecific atom extends not only to the physical mixing of the compoundwith other materials, but also to any physical and/or chemicalinteraction which may result upon introduction of the compound, or uponstanding.

Many fuel oil additives are known in the art and may be used to form theadditive composition into which the compound is incorporated. Suchadditives include for example the following; detergents, antioxidants,corrosion inhibitors, dehazers, demulsifiers, metal deactivators,antifoaming agents, cetane improvers, combustion improvers, dyes,package compatibilisers, further lubricity additives and antistaticadditives. Cold flow-improving additives may also be present.

D. The Additive Concentrate Composition

The concentrate may be obtained by incorporating the compound definedunder the first aspect, or the additive composition, into amutually—compatible solvent therefore. The resulting mixture may beeither a solution or a dispersion, but is preferably a solution.Suitable solvents include organic solvents including hydrocarbonsolvents, for example petroleum fractions such as naphtha, kerosene,diesel and heating oil; aromatic hydrocarbons such as aromaticfractions, eg. those sold under the ‘SOLVESSO’ tradename; and paraffinichydrocarbons such as hexane and pentane and isoparaffins.

Further solvents include oligomers and hydrogenated oligomers of alkenessuch as hydrogenated decene-1 dimer or trimer. Also useful are alcoholsand esters especially higher alcohols such as liquid alkanols having atleast eight carbon atoms. An especially useful solvent is isodecanol.Mixtures of such solvents maybe used in order to produce amutually—compatible solvent system.

The concentrate may contain up to 80% by weight, for example 50%, ofsolvent.

The concentrate is particularly convenient as a means for incorporatingthe additive composition into fuel oil where despite the presence of thecompound, the co-presence of other desired additives in the compositiondemands an amount of solvent in order to impart handleability. However,concentrates comprising the compound as sole additive may also be used,especially where small quantities of is the compound are required andthe equipment present for introduction of the additive lacks thenecessary accuracy to measure or handle such small volumes.

Where the fuel oil composition is produced by incorporation of theadditive composition or concentrate, the amount used of either of thesecompositions will be such as to ensure the incorporation to the fuel oilof the requisite amount of the compound. For example, however, where theadditive composition or concentrate is used, the amount will usually bein the range of 1 to 5,000 ppm of the composition (active ingredient) byweight per weight of fuel, especially 10 to 2000 ppm such as 50 to 500ppm.

As indicated above, the compound defined under the first aspect, and theadditive composition and concentrate defined under the second aspect,find application in low sulphur fuel oils.

A further aspect of this invention is therefore the use of the compound,or the additive composition or concentrate, in a liquid hydrocarbonmiddle distillate fuel oil, having a sulphur concentration of 0.2% byweight or less, per weight of fuel, particularly to improve thelubricity thereof. This invention also provides a method for improvingthe lubricity of a liquid hydrocarbon middle distillate fuel oil havinga sulphur concentration of 0.2% by weight based on the weight of fuel,comprising the addition thereto of the additive composition orconcentrate, or of the compound.

THE COMPOUND OF THE THIRD ASPECT

The compound claimed under the third aspect comprises one or morehydroxyl derivatives of the formula —OR′ wherein R′ is as defined inrelation to the first aspect but is not hydrogen. Such materials mayshow good performance as lubricity improvers and as detergents and/ordispersants in low sulphur middle distillate fuel oils.

What is claimed is:
 1. A fuel oil composition exhibiting improvedlubricity obtainable by the addition of 0.5 to 1000 ppm of a lubricityimproving compound comprising two or more aromatic ring systems, whereineach one of the ring systems bears, as substituents: (i) one or morehydrocarbon groups imparting oil solubility to the compound, and (ii)one or more hydroxyl groups or derivatives thereof or both, and (iii)one or more amine salt groups, to a major proportion of a liquidhydrocarbon middle distillate fuel oil having a sulphur concentration of0.2% by weight or less, based on the weight of fuel.
 2. A fuel oilcomposition obtainable by the addition to a liquid hydrocarbon middledistillate fuel oil having a sulphur concentration of 0.2% by weight orless, based on the weight of fuel, of an additive composition orconcentrate into which has been incorporated a compound comprising twoor more aromatic ring systems, wherein each one of the ring systemsbears, as substituents; (i) one or more hydrocarbon groups imparting oilsolubility to the compound, and (ii) one or more hydroxyl groups orderivatives thereof or both, and (iii) one or more amine salt groups. 3.The composition of claim 1 wherein the compound has the general formula(I):

wherein Ar represents an aromatic ring system; B represents ahydrocarbon group (i); OR′ represents a hydroxyl group or derivativethereof (ii) wherein R′ represents hydrogen, or a hydrocarbyl group, ora group of the formula

wherein M represents an oxygen atom or an NH group and n represents anumber from 1 to 50, and wherein R′ may be bonded either directly to theoxygen depending from the ring system or indirectly via a linking group;—COO^(⊖⊕)NR^(2′)R^(3′)R^(4′)R^(5′) represents an amine salt group (iii)wherein R^(2′), R^(3′), R^(4′) and R^(5′) each independently representhydrogen or a hydrocarbyl group or a poly(alkyleneoxy) alkyl orpoly(alkyleneamino)alkyl group, optionally substituted by one or moreheteroatom-containing groups, and A represents a group of the formula(II):

wherein Ar, B, R′, R^(2′), R^(3′), R^(4′) and R^(5′) are as definedabove, and A′ and A″ each independently represent hydrocarbylene groups,and wherein v represents an integer in the range of from 0 to 10, wrepresents an integer in the range of from 1 to 3, and x, y and z eachindependently represent an integer in the range of from 1 to
 3. 4. Thecomposition of claim 1 wherein each aromatic ring system of the compoundis a single, six-membered ring.
 5. The composition of claim 1 whereinthe amine salt group is derivable from an alkylene diamine orpolyalkylene polyamine or mono- or dialkylamine.
 6. A method forimproving the lubricity of a liquid hydrocarbon middle distillate fueloil having a sulphur concentration of 0.2% by weight or by less based onthe weight of fuel, comprising the addition thereto of 0.5 to 1000 ppmof a compound comprising two or more aromatic ring systems, wherein eachone of the ring systems bears, as substituents; (i) one or morehydrocarbon groups imparting oil solubility to the compound, and (ii)one or more hydroxyl groups or derivatives thereof or both, and (iii)one or more amine salt groups.
 7. A method for improving the lubricityof a liquid hydrocarbon middle distillate fuel oil having a sulphurcontent of 0.2% by weight or less based on the weight of the fuel,comprising adding thereto of an additive composition into which has beenincorporated a compound comprising two or more aromatic ring systems,wherein each one of the ring systems bears, as substituents; (i) one ormore hydrocarbon groups imparting oil solubility to the compound, and(ii) one or more hydroxyl groups or derivatives thereof or both, and(iii) one or more amine salt groups, such that the fuel contains 0.5 to1000 ppm of the compound.
 8. A method for improving the lubricity of aliquid hydrocarbon middle distillate fuel oil having a sulphur contentof 0.2% by weight or less based on the weight of the fuel comprisingadding thereto of a concentrate into which has been incorporated acompound comprising two or more aromatic ring systems, wherein each oneof the ring systems bears as substituents; (iii) one or more hydrocarbongroups imparting oil solubility to the compound, and (v) one or morehydroxyl groups or derivatives thereof or both, and (vi) one or moreamine salt groups, such that the fuel contains 0.5 to 1000 ppm of thecompound.